Clarify composites in part 2

[eelstork]

After poking around to see how devs engage with BTs, I find that part 2 ideally should have a much cleaner structure where each status function (except terminals) is either a sequence or a selector.
The same applies to the example on active-logic-cs, one which is actually off-putting in that it is, well. Overly complex.
Aside - a galore showing small snippets demonstrating features; also a long overdue cheat-sheet/quick-ref section (file upstream)